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Forum > Failed Smog Test > Question

1992 GMC Suburban 2500 has high CO because of loose spark plug.

Can a loose sparkplug and two connection to the distibutor they were in the wrong places) Could it cause high percent of CO?
Answer:

Yes, absolutely. A loose spark plug wire will cause not only high CO, but high HC as well. You want to get that fixed and have your Suburban re-tested after. The emissions numbers will change. If your GMC still fails the smog check, you can then go in to a detailed diagnosis. posted by SmogTips Support

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